then Firefly will automatically compute and punch the differences between two consecutive densities. This may require setting properiroot or istate keyword depending on particular computational method.

Unfortunately this does not work well for TDDFT as normally one is interested in difference of relaxed density and KS density while Firefly would computes two differences: one between non-relaxed TDDFT density and KS densities and secondbetween relaxed and non-relaxed TDDFT densities. To make this work one needs to specify proper nstate and istate in $tddft group and adds tdprp=.t. to $dft group.

As to second part of your question, I'd suggest you to use gOpenMol to manipulate cubes and plt files. First, gOpenMol distribution contains gamess2plt utility that was developed to extract $CUBE information from the PC GAMESS/Firefly punch files and convert them to plt files. Second, there is an utility called contman that can be used to add or subtract two plt files. Finally, plt files can be visualised by either gOpenMol or by (the better way) Chimera and probably by some other visualizer. In addition, powerful general purpose vilualizers like VisIt and ParaView accepts cube files and can manipulate them.

All the best,Alex

On Wed Jun 8 '16 4:09pm, Michal Krompiec wrote---------------------------------------------->Hi, how can I generate a CUBE file for the difference in electron density between a chosen excited state and the ground state? If it is not possible directly, can I subtract the respective CUBEs with some external software? (other than ChemCraft)